He said this was bringing fresh air through, and that the worst of the pollution should be gone by dawn tomorrow.

How Sahara dust came to Norfolk

The region’s ambulance service had a slight increase in 999 calls yesterday.

A spokesman for the East of England Ambulance Service NHS Trust said: “Demand on Wednesday was up by 6% in comparison to recent Wednesdays.

“But although we were busy first thing in the morning and then early evening, it is difficult to say the air pollution was a factor as the number of patients with breathing problems and associated sickness was not markedly high.

“It’s really important that people with long-term conditions which could be exacerbated by the air quality take extra caution to help prevent their health getting worse.”

The expert’s view

Record levels of air pollution will continue to plague the UK, experts have warned.

A perfect storm of dust from the Sahara, emissions from the Continent, low south-easterly winds and domestic pollution has caused air quality to plummet and the smog-like conditions are not expected to clear until tomorrow.

Around two-thirds of the 3.6 million people with asthma find that air pollution makes their asthma worse.

The advice, from Public Health England (PHE), Asthma UK and Defra, comes after a warning that parts of England are experiencing the highest level of air pollution ever recorded by Defra.

Some schools in London have banned pupils from outdoor playgrounds to reduce their exposure to the fog.

The decision was supported by Professor Frank Kelly, professor of environmental health at King’s College London and a member of the Department of Health’s Committee on the Medical Effects of Air Pollution, who said it would help reduce long-term harm to children.

“As a general response this is a good approach as children tend to run around outside and therefore breathe deeper,” he told the Guardian.

“Thus, on days like this they will be aspiring a lot more pollution if outdoors than when they are breathing normally (hopefully) inside.”

Prof Kelly added: “Whether home-produced or arriving from the continent, the tiny particles we take into our bodies with each breath cause immediate problems for some individuals such as those with asthma and contribute to longer term problems for most of us in the form of heart disease and stroke.

“For those who are sensitive to air pollution, it’s important they are provided with accurate forecasts of when air quality will deteriorate so they can plan their activities to reduce exposure, perhaps by taking different routes to work or school or avoiding strenuous exercise on those days.

Kay Boycott, chief executive of Asthma UK, said: “The two-thirds of people with asthma who find that air pollution makes their asthma worse will be at an increased risk of an attack following the alarming Defra warning of high pollution levels around the country.

“Asthma UK warns the 3.6 million people at increased risk to be sure they always have a working blue reliever inhaler on them and take their preventer inhalers as prescribed.”

Paul Cosford, director of health protection at PHE, told BBC Radio 4’s Today programme that the air pollution was a “serious issue” but should be kept in perspective.

“It’s a small number of days of very high air pollution levels,” he said. “The pollution will go down towards the end of the week.”

The Queen Elizabeth Hospital in King’s Lynn and the Norfolk and Norwich University Hospital in Norwich reported no change in admissions of people with breathing problems, while the James Paget University Hospital in Gorleston reported a slight increase.

In King’s Lynn, one of the worst-hit area, the smog was clearing this morning, with a westerly wind taking it out to sea.

Lowestoft, the most easterly part of the region, had no smog today.

A Norfolk county council spokesman said 12 schools have contacted the authority for advice today.

They issued advice in line with national Defra advice, stating: “Those with existing health conditions such as heart and lung problems should avoid strenuous activities outdoors

“People who use a reliever inhaler should make sure that they carry it with them. If they feel that their conditions are worsening then they should contact their GPs

“It would be advisable for schools to pay particular attention to pupils with asthma or respiratory conditions etc as they may be more vulnerable. In severe cases, they may want to consider avoiding outdoor activities for those pupils.”

Defra - Department for Environment, Food and Rural Affairs - ranks air pollution from one to 10, with one being the lowest and 10 the highest.

Parts of East Anglia were level 10 yesterday with vulnerable people being warned by experts to cut down on the amount of activity they took outside.

Diss, Wymondham, Thetford, King’s Lynn and Swaffham were all ranked level 10 at 5pm yesterday, with Norwich and Dereham ranked level nine, Great Yarmouth eight, and Cromer and Sheringham four.

High levels of pollution are also forecast for East Anglia today, but the exceptional levels of pollution are expected to ebb away by tomorrow with cleaner south-westerly winds.

A Defra spokesman said the elevated pollution levels were caused by light easterly winds continuing to bring in pollutants and allowing local pollutants to remain close to source, and dust which has blown up from the Sahara desert.

The air pollution has particularly affected asthmatics and other people with lung and heart problems, and older people have been told to avoid strenuous exercise or activity.

However, the air pollution has not caused an influx of patients at the region’s hospitals or doctors’ surgeries, with schools, running clubs and hospitals seemingly taking it in their stride.

A spokesman for Southgates medical and surgical centre in Goodwins Road, King’s Lynn, said they had not seen an increase in the number of patients with illnesses related to air pollution.

And the Norfolk and Norwich University Hospital, Gorleston’s James Paget hospital and King’s Lynn’s Queen Elizabeth hospital have not experienced an increase in patients.

Meanwhile, Wally Oliver, chairman of the West Norfolk Athletic Club, based at Lynnsport, said athletes had not been told to take any extra precautions.

He said: “We have not done anything different because of the air pollution. We train in the evenings, when the pollution’s probably not as bad. There were no problems reported at the training session on Monday night.”

And spokesmen for Springwood High School Academy in King’s Lynn and City Academy Norwich said they had not changed their activities or cut back on PE classes because of the air pollution.

Sotiris Vardoulakis, head of air pollution at Public Health England’s centre for radiation, chemical and environmental hazards, said: “Whilst most people will not be affected by short-term peaks in air pollution, some individuals, particularly vulnerable groups such as those with existing heart or lung conditions, may experience increased symptoms.

“On occasions where levels are high, adults and children with lung problems, and adults with heart problems, should reduce strenuous physical exertion, particularly outdoors, and particularly if they experience symptoms.

“People with asthma may find they need to use their reliever inhaler more often. Older people should also reduce physical exertion.

Frank Kelly, professor of environmental health at King’s College London, said: “Whether home-produced or arriving from the continent, the tiny particles we take into our bodies with each breath cause immediate problems for some individuals such as those with asthma and contribute to longer term problems for most of us in the form of heart disease and stroke.

“For those who are sensitive to air pollution, it’s important they are provided with accurate forecasts of when air quality will deteriorate so they can plan their activities to reduce exposure, perhaps by taking different routes to work or school or avoiding strenuous exercise on those days.

“Even those who do not feel any particular sensitivity to air pollution can benefit from such avoidance techniques but they will have to wait several decades to see the benefit.”

Saharan dust is lifted by strong winds and can reach very high altitudes, from where it can be transported worldwide by the wind.

The dust gets caught in rain droplets in clouds, falling to the ground in so-called ‘dirty rain’. When the water evaporates, a thin layer of dust is left on surfaces, like cars.

Saharan dust landing on Norfolk has, however, been good news for car wash businesses, with many noticing a large increase in the amount of customers coming their way. Car salesmen have also reported layers of dust on all their vehicles.

How have you been affected by air pollution? Email reporter David Bale at david.bale2@archant.co.uk

While I am sorry for people whose breathing problems have been made worse by the so-called smog, real Saharan dust would cause nil visibility and get into everything. The air would be reddish-brown. We can't see the worse problem of toxic particles in the air from vehicle fumes - this is all-pervasive, colourless, and far more damaging.